The present invention relates to a ball bearing and, more particularly, a precision linear bearing which can be translated along a shaft and comprises closed travel circuits provided with balls. Each closed circuit comprises two longitudinal portions connected at their ends by curved portions. The balls located in a first longitudinal portion of each circuit support the load of the bearing on the shaft and are recycled, upon translation in the active portion, travelling in the curves and in the opposite direction in the other longitudinal portion.
Such linear bearings frequently replace plan guides and have the advantage of low friction, good precision and long life, although anti-friction bearings are preferable to plain bearings for movements of rotation.
In the prior art there are two main types of configuration of linear bearings, one closed and tubular and the other open, with a longitudinal angular passage provided over the entire length of the bearing and enabling it to operate on a supported shaft.
The bearings known up to the present time are of relatively complicated construction, resulting from the assembling of parts manufactured separately by processes such as turning, swaging, milling, cutting, broaching, with hardening, straightening or other treatments, in which only the balls are readily obtained on the market. Other bearings require very complicated and expensive specific tooling.
Germany Patent No. A-2,116,955 describes a linear bearing formed of an outer sleeve positioning inner parts which form ball circuits and are held in place by the sleeve and by special rings engaged in grooves provided in the sleeve. In the active longitudinal portion, a needle is arranged radially with respect to the balls in contact with the shaft in order to favor the travel of the balls and urge them in the direction towards the shaft. This manner of construction has the drawback of requiring several manufactured parts of different shape and material; furthermore, this embodiment does not make it possible to obtain an open bearing configuration.
Swiss Patent No. 654,886 discloses a linear bearing formed of a solid part which maintains needles above the ball circuits. Although, in this case there is a base construction of needles held on a single piece, this embodiment represents a large investment since the molding equipment is complicated, sensitive and comprises six or even eight rows operating semi-radially in order to obtain all the forms of the element around a bipartite core. Furthermore, this solid construction places the needles in an excessively radially rigid fashion, which creates problems in introducing the bearing in its place and makes difficult an open configuration embodiment which, on the other hand, will deform towards the inside. Furthermore, it is not possible to produce this bearing with a closed outer surface without adding other additional parts.
The prior art also contains other embodiments all of which require special, sophisticated tools. These manners of construction call for substantial investments, in addition to the deficiencies already indicated in the case of open configuration bearings.